Photothermal properties of plasmonic nanoshell-blended nanofluid for direct solar thermal absorption.

The excitation of localized surface plasmon at the metal nanoparticles can significantly enhance the absorption of solar energy. However, the absorption peak is sharp at the resonant frequency. To achieve a broadband absorption, the blended nanofluid formed by SiO2 /Ag nanoshells of different core size and shell thickness is employed. The blended nanofluid has a good solar absorption property, whose extinction spectrum matches the solar spectrum well. The transient temperature response of the nanofluid is simulated. It is found that the photothermal performance of the solar thermal collector is related to the geometric parameters and operation conditions of the solar collector, and the optical and thermophysical properties of nanofluid. As the flow velocity increases, the outlet temperature is gradually reduced. But, the collector efficiency is increased since less heat is lost to the environment via convection as nanofluid flows fast in the channel. In order to obtain a large outlet temperature at high velocity, it can be considered to elongate the channel length. Due to the strong extinction properties of the blended nanofluid, the required volume fraction can be significantly reduced, only 1/10 of that of Ag nanofluid for an equal temperature increases.